1. Field of the Invention
The present invention relates to a chemically amplified resist composition useful for a micro-engineering process using various radiations including far ultraviolet ray (e.g., KrF excimer laser and ArF excimer laser), X-ray (e.g., synchrotron radiation) and charged particle beams (e.g. electron beam) and, more particularly, to a chemically amplified resist composition comprising (A) a polymer for resist having an acid labile group, (B) a photoacid generator, and (C) a low molecular weight additive for increasing dry etching resistance and resolution of the pattern.
2. Description of the Related Art
In the fabrication of semiconductor devices, a resist is applied on a substrate such as silicon wafer to form a coating and exposed to radiations to form a pattern, after which the resist is developed to form a positive or negative pattern, i.e., an image is created by lithography.
As the LSI and VLSI technologies in the fabrication of semiconductor integrated circuits tend toward higher integration, higher density, miniaturization and higher speed, a rule of submicron (less than 0.2 micron) is required for the fineness of pattern. Accordingly, the lithography light sources are shifting towards shorter wavelength from the existing g- or i-line band and there is an increasing interest in the lithography using far UV radiations, KrF or ArF excimer laser, X-ray or electron beams.
Near UV radiations including i-line have been mainly used in the existing lithography process but are known insufficient to form sub-quarter (0.25) micron patterns. For the formation of sub-quarter micron patterns, the attention is focused on radiation sources in the shorter wavelength band including far UV radiations such as excimer lasers, X-ray and electron beams, and particularly KrF or ArF excimer laser.
Resist compositions suitable for the excimer laser lithography comprise a polymer component having an acid labile group, a component generating an acid upon irradiation with a radiation (hereinafter, referred to as xe2x80x9cphotoacid generatorxe2x80x9d), and a solvent. Such resists comprising the resist compositions undergo chemical amplification due to the photoacid generator in the lithography and will be hereinafter referred to as xe2x80x9cchemically amplified resistxe2x80x9d.
For example, chemically amplified resist compositions containing a polymer having a ter-butyl ester group of carboxylic acid or a ter-butylcarbonyl group of phenol, and a photoacid generator are disclosed in Japanese Patent Application Kokoku No. 2-27,660. These resist compositions have such an advantage that the catalytic action of the acid generated under irradiation of a radiation causes the tert-butyl ester group or tert-butylcarbonyl group of the polymer decomposed to leave a hydroxyl group, which makes the exposed area of the resist very soluble in an alkaline developing solution.
However, chemically amplified resists used in the KrF excimer laser lithography are mostly composed of a phenol resin as a base material containing aromatic rings and unsuitable for use in the ArF excimer laser because the aromatic rings in the phenol resin absorb lots of the ArF excimer laser. In an attempt to overcome this problem, many studies have been made on polyacrylate derivatives as a matrix resin having less absorption of the ArF excimer laser than the phenol resin (See. Japanese Patent Laid-Open Kokoku No. 4-226,461, Proc. SPIE, 1996, vol. 2724, p. 377).
Polyacrylate absorbs less radiation having a wavelength falling within the ArF excimer laser region but is adversely inferior in the dry etching resistance. To solve this problem, there have recently been made many studied on the method for improving the etching resistance of the resist with an alicyclic derivative introduced to the side chain of the polyacrylate, in which case the hydrophobic property of the alicyclic derivative deteriorates the affinity to the developing solution. The adhesion between the resist and the substrate is an important factor in formation of less than 0.2 micron patterns. So, the existing polyacrylate matrix resin contains a carboxylic acid at the side chain in order to enhance the adhesion to the substrate (See. Proc. SPIE, 1997, vol. 3049, p. 126). However, an excess of the carboxylic acid increases the solubility of the polyacrylate resin in the alkaline aqueous solution and causes a need of varying the concentration of the alkaline developing solution.
An example of matrix resin that has improved dry etching resistance and hydrophilic property may include a copolymer of anhydrous maleic acid and olefin (See. Proc. SPIE, 1997, vol. 3049, p. 92). The anhydrous maleic acid possesses the hydrophilic property and acts as a promoter enabling copolymerization with the olefin monomer at low temperature and low pressure. Also, the olefin monomer may contain various substituents at the side chain to enhance dry etching resistance and resolution (See. Proc. SPIE, 1998, vol. 3333, p. 463).
Recently, low molecular weight additives for use in the resist composition containing a copolymer resin of anhydrous maleic acid and olefin monomers are being watched with keen interest so as to improve the residual coating property, increase dry etching resistance and reduce refining effect in the formation of patterns (Korean Patent Laid-Open No. 98-064842; and Proc. SPIE, 1998, vol. 3333, p. 73).
It is, therefore, an object of the present invention to provide a chemically amplified photoresist sensitive to the far UV radiations including KrF or ArF excimer laser and, more particularly, a chemically amplified resist composition which has a high transparency to the ArF excimer laser to provide high resolution and sensitivity of the photoresist and is excellent in adhesion to the substrate, dry etching resistance and developing property due to a low molecular weight additive having a ring structure with an acid-labile acetal or ketal group.
To achieve the above object of the present invention, there is provided a chemically amplified positive photoresist composition comprising:
a multi-component copolymer represented by the formula 1 and having a polystyrene-reduced weight average molecular weight (Mw) of 3,000 to 50,000 and a molecular weight distribution (Mw/Mn) of 1.0 to 3.0;
a low molecular weight additive represented by the formula V;
an acid generator; and
a solvent,
[Formula 1]
wherein X and Y independently comprise a repeating unit selected from the group consisting of monomers represented by the formulas (II), (III) and (IV): 
wherein R1 is a hydrogen atom, a normal, branched, monocyclic or polycyclic alkyl group having 1 to 20 carbon atoms, or a normal, branched, monocyclic or polycyclic alkyl carbonyl group having 1 to 20 carbon atoms, including acetyl group, t-butyl oxycarbonyl group, cyclohexane carbonyl group, adamanthane carbonyl group and bicyclo[2,2,1]heptane methyl carbonyl group; R2 is a hydrogen atom, a hydroxyl group, a carboxyl group, an alkyl or alkoxy group having 1 to 20 carbon atoms, an alkyl or alkoxy group containing a hydroxyl or carboxyl group, a normal or branched alkyloxycarbonyl or alkoxyalkylcarbonyl group, or a monocyclic or polycyclic alkyloxycarbonyl group; R3 is a hydrogen atom, or a normal, branched, monocyclic or polycyclic alkyl group having 1 to 20 carbon atoms, including methyl group, ethyl group, t-butyl group, isopropyl group, adamanthyl group, and bicyclo[2,2,1]heptane methyl group; and l, m, n and o are independently a number representing the repeating unit of the polymer and satisfying 0xe2x89xa6l/(l+m+n+o)xe2x89xa60.5, 0xe2x89xa6m/(l+m+n+o)xe2x89xa60.5, 0xe2x89xa6n/(l+m+n+o)xe2x89xa60.35, 0.4xe2x89xa6o/(l+m+n+o)xe2x89xa60.6, and 0.15xe2x89xa6(l+m)/(l+m+n+o)xe2x89xa60.5,
[Formula V]
wherein R4 and R5 are the same as or different from each other and each represents a normal, branched, monocyclic or polycyclic alkyl group having 1 to 20 carbon atoms; and R6 is a hydrogen atom, or a normal, branched, monocyclic or polycyclic alkyl or alkoxy group having 1 to 20 carbon atoms.
To improve the drawbacks of the related art chemically amplified positive resist in regard to adhesion to substrate, dry etching resistance and developing property, the invention provides a novel chemically amplified positive resist composition having a ring structure at the main chain comprising anhydrous maleic acids and norbornene derivatives to enhance dry etching resistance, a hydroxyl group as a repeating unit at the side chain to enhance adhesion to substrate, and optionally various acid-labile groups at the side chain to improve sensitivity and resolution of the resist. In particular, the chemically amplified positive resist composition further comprises a low molecular weight additive containing an acid liable group whose action enhances the dissolution-inhibiting effect on the unexposed region.
(A) Polymer
The polymer used in the present invention has a repeating unit containing an anhydrous maleic acid, and a norbornene or norbornene carboxylic acid derivative, an anhydrous norbornene carboxylic acid derivative, or a norbornene derivative having hydroxyl groups or acid labile groups attached to the side chain. Also, the polymer according to the present invention is in itself insoluble or hardly soluble in an alkaline aqueous solution and contains at least one protective group decomposable by the photoacid generator.
The alkali-solubility of the polymer can be varied depending on the content of the acid labile groups decomposable by the photoacid generator. As such, various polymers are obtained depending on the type and content of the norbornene derivative in the main chain. Using this polymer, the resist composition has excellent dry etching resistance and adhesion to substrate, as well as enhanced resolution and heat resistance.
The polymer used in the present invention is a multi-component copolymer having a repeating unit represented by the formula 1.
Monomers represented by the formulas (II), (III) and (IV) contain at least one hydroxyl group, carboxyl group or acid labile group, and a hydrophobic group having a straight or ring chain in the molecule, so that the polymer using the monomers increases the dissolution-inhibiting effect on the unexposed region of the resist with enhanced dry etching resistance.
The monomer represented by the formula (II) is 3-bicyclo[2,2,1]hept-5-en-2-yl-3-hydroxy-propionic acid-tert-butylester (hereinafter, referred to as xe2x80x9cBHPxe2x80x9d), or derivatives thereof. Specific examples of the monomer may include: 
The monomer represented by the formula (III) is a norbornene carboxylic acid, or derivatives thereof, and specific examples of the monomer may include: 
The monomer represented by the formula (IV) is an anhydrous norbornene carboxylic acid, or derivatives thereof, and specific examples of the monomer may include: 
The polymer represented by the formula 1 can be prepared by multi-copolymerization of a monomer selected from the norbornene derivatives having theformulas (II), (III) and (IV), a norbornene and an anhydrous maleic acid.
In selection of the norbornene derivative X or Y in the formula 1, it is desirable that the norbornene derivative X in the formula 1 contains a hydroxyl or carboxyl group as represented by the formula (II-9), (III-3) or (IV-1) and that the norbornene derivative Y contains neither hydroxyl nor carboxylic group but has an acid labile group.
Examples of the multi-component copolymer prepared by the above-stated procedure may include the following polymers, wherein the content of the repeating unit in the resin can be property varied in consideration of sensitivity, adhesion to substrate and resolution of the resist: 
wherein R1, R2, R3, l, m, n and o are as defined above.
The multi-component copolymer may include a block copolymer, a random copolymer or a graft copolymer and, preferably, an alternating copolymer or random copolymer of anhydrous maleic acids and norbornene derivatives.
The polymer represented by the formula 1 can be prepared by a known polymerization reaction and, preferably, solution polymerization using a radical polymerization initiator. Examples of the radical polymerization initiator may include, if not limited to, azo compounds such as azo-bis(isobutyronitrile) (AIBN), dimethyl 2,2xe2x80x2-azo-bis(isobutyrate), 1,1xe2x80x2-azo-bis(cyclohexane-1-carbonitrile), 2,2xe2x80x2-azo-bis(2-methylbutyronitrile), 2,2xe2x80x2-azo-bis(2,4-dimethylvaleronitrile), azo-bis(isocapronitrile) and azo-bis(isovaleronitrile); benzoyl peroxide (BPO); lauryl peroxide; and tert-butyl hydroperoxide.
The polymerization reaction includes mass polymerization, solution polymerization, suspension polymerization, mass-suspension polymerization and emulsion polymerization. Examples of suitable solvent for solid polymerization may include at least one selected from the group consisting of benzene, toluene, xylene, halogenated benzene, diethyl ether, tetrahydrofuran, 1,4-dioxane, acetates, esters, lactones, ketones, and amides.
The polymerization temperature of the polymers represented by the formula 1 is properly controllable depending on the type of the polymerization initiator. For example, the polymerization temperature is preferably in the range from 60 to 80xc2x0 C. in the presence of azo-bis(isobutyronitrile) used as a polymerization initiator.
The molecular weight and the molecular weight distribution of the polymers are also properly controllable depending on the added amount of the polymerization initiator and the polymerization temperature and time.
Preferably, non-reactive monomers and by-products remaining in the reaction mixture after the completion of the polymerization reaction are removed by the precipitation method using an appropriate solvent. The precipitating solvent can be selected depending on the type of the polymerizing solvent and the structure of the monomer used. Specific examples of the suitable precipitating solvent may include methanol, a mixed solvent of methanol and distilled water, ethanol, isopropylalcohol, a mixed solvent of isopropylalcohol and hexane, hexane, and ether.
The polymers represented by the formula 1 have a polystyrene-reduced weight average molecular weight (hereinafter, referred to as xe2x80x9cMwxe2x80x9d) measured by gel permeation chromatography (GPC) in the range of 1,000 to 100,000, and preferably 3,000 to 50,000 in consideration of sensitivity, developing and coating properties, and heat resistance of the resulting photoresist.
The polymers whose Mw is smaller than 1,000 are hard of forming coatings on the substrate with a deterioration of coating and developing properties, and those having a Mw larger than 100,000 reduce the sensitivity, resolution and developing property of the resist. The molecular weight distribution of the polymers is preferably in the range from 1.0 to 5.0 and, more preferably, from 1.0 to 3.0.
The polymers synthesized were determined in regard to molecular weight (Mw) and molecular weight distribution by gel permeation chromatography using an 1100 series instrument (supplied by HP) and a TriSEC detector (supplied by Viscotek) equipped with one G2500HXL column and one G4000HXL column in tetrahydrofuran (as an eluant) at 40xc2x0 C. and at a flow rate of 1.0 ml/min. The molecular weight values reported are reduced in relation to a monodispersion polystyrene standard.
The polymers can be used alone or in combination of two or more of them in the resist composition of the invention.
(B) Photoacid Generator
Examples of suitable photoacid generator for the composition of the present invention may include onium salts such as iodonium salt, sulfonium salt, phosphonium salt, diazonium salt and pyridinium salt and, particularly preferably, triphenylsulfonium triplate, diphenyl(4-methylphenyl)sulfonium triplate, diphenyl(4-t-butylphenyl)sulfonium triplate, diphenyl(4-methoxyphenyl)sulfonium triplate, diphenyl(naphthyl)sulfonium triplate, dialkyl(naphthyl)sulfonium triplate, triphenylsulfonium nonaplate, diphenyl(4-methylphenyl)sulfonium nonaplate, diphenyl(4-t-butylphenyl)sulfonium nonaplate, diphenyl(4-methoxyphenyl)sulfonium nonaplate, diphenyl(naphthyl)sulfonium nonaplate, dialkyl(naphthyl)sulfonium nonaplate, triphenylsulfonium hexafluoroantimonate, diphenyliodonium triplate, diphenyliodonium methylbenzene sulfonate, bis(cyclohexylsulfonyl)diazomethane, and bis(2,4-dimethylphenylsulfonyl)diazomethane.
Unlike the related art photoacid generators, the onium salts represented by the formula 3 acts as a dissolution inhibitor in the exposed region of the resist and a dissolution enhancer in the exposed region, thereby making the exposed region dissolved more readily than the unexposed one.
[Formula 3]
wherein R7 and R8 are independently a normal, branched, monocyclic or polycyclic alkyl group, or an aryl group; R9 and R10 are independently hydrogen, an alkyl group, or an alkoxyl group; and p is an integer from 0 to 14.
An amount of the photoacid generator contained in the resist composition of the present invention is in the range of 0.1 to 30 parts by weight and preferably 0.3 to 10 parts by weight based on 100 parts by weight of the polymer. Those photoacid generators can be used alone or in combination of two or more of them in the resist composition of the invention.
(C) Low Molecular Weight Additives
The low molecular weight additives used in the present invention provide such a ring structure in the molecule as to increase the dry etching resistance, improve the residual coating property at the unexposed region and promote dissolution in an alkaline developing solution by the action of the acid at the exposed region, thereby much enhancing dissolution contrast in the development step and verticality of the side walls of the resist pattern.
Alicyclic derivatives with an acid-labile leaving group are particularly suitable as a compound readily decomposable to acids to promote the dissolution rate in the developing solution.
The low molecular weight additives used in the present invention are carboxylic acid derivatives represented by the formula 2.
Special examples of the carboxylic acid derivatives having the formula 2 may include: 
These low molecular weight additives can be used alone or in combination of two or more of them in the resist composition of the invention.
An amount of the low molecular weight additives contained in the resist composition of the invention is in the range of 3 to 50 parts by weight and preferably 5 to 40 parts by weight based on 100 parts by weight of the polymer. The low molecular weight additives in an amount of less than 3 parts by weight hardly act on the resist. With an amount of the low molecular weight additives exceeding 50 parts by weight, the resulting resist will have a great deterioration of adhesion to the substrate and coating property.
The resist composition of the invention may optionally contain other additives. For example, these optional additives include surfactant, halation inhibitor, adhesion promoter, storage stabilizer and antifoaming agent.
Specific examples of suitable surfactant are polyoxylauryl ether, polyoxystearyl ether, polyoxyethylene oleyl ether, and polyethylene glycol dilaurylate. An amount of the surfactant contained in the resist composition of the invention is preferably less than 2 parts by weight based on 100 parts by weight of the polymer.
Also, the resist composition of the invention may optionally contain a basic compound in order to prevent diffusion of acids generated under irradiation of a radiation. An amount of the basic compound contained in the resist composition of the invention is preferably in the range of 0.01 to 5 parts by weight based on 100 parts by weight of the polymer. If the amount of the basic compound exceeds the above range, diffusion of the acids decreases with a deterioration of sensitivity of the resist.
Preferably, the resist composition of the invention is dissolved in a solvent having appropriate vaporization rate and viscosity prior to use in order to obtain a uniform and smooth coating film.
Examples of suitable solvent may include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, methylcellusolve acetate, ethylcellusolve acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, methyl ethyl ketone, cyclohexanone, methyl 2-hydroxypropionate, ethyl 2-hydroxypropionate, 2-heptanone, ethyl lactate, and xcex3-butyrolactone. These solvents can be used alone or in combination of two or more of them in the resist composition of the invention. The amount of the solvent used in the resist composition is properly controllable depending on the properties of the solvent, i.e., volatility and viscosity so as to form a uniform resist film on a wafer.
The resist composition of the invention is prepared in the form of a solution, applied to the wafer substrate and dried to form a resist film. In applying the composition on the wafer, the resist solution is filtered and applied to the substrate by a spin coating, flow coating, roll coating or the like.
Subsequently, the resist film is partially subjected to radiations in order to form fine resist patterns. Examples of suitable radiations may include, if not limited to, UV radiations (e.g., i-lines), far UV radiations (e.g., KrF excimer laser and ArF excimer laser), X-rays, and charged particle rays (e.g., electron rays). The radiations can be selected depending on the type of the photoacid generator. Following the irradiation of radiations, the resist film is optionally subjected to heat treatment in order to enhance the sensitivity.
In the subsequent development step, the irradiated resist film is developed with a developing solution, examples of which may include aqueous solutions containing sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, sodium methasilicate, ammonia water, ethyl amine, n-propyl amine, triethylamine, tetramethylammonium hydroxide, or tetraethylammonium hydroxide. Among these developing solutions, tetramethylammonium hydroxide is most preferable. Optionally, the developing solution further contains additives such as surfactant or aqueous alcohols.
The present invention will be described in greater detail by way of the following examples, which are not intended to limit the present invention.